CLAIM OF PRIORITY

This application claims the priority of U.S. non-Provisional Application Serial No. 13/949,736 entitled "SUPPRESSION OF SPURIOUS HARMONICS

GENERATED IN TX DRIVER AMPLIFIERS" and filed on July 24, 2013, which is assigned to the assignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

[0001] The present disclosure relates to electronic circuits, and more particularly to a transmitter used in such circuits.

[0002] A wireless communication device, such as a cellular phone, includes a transmitter for transmitting signals and a receiver for receiving signals. The receiver often downconverts an analog radio frequency (RF) signal to an intermediate frequency (IF) signal which is filtered, amplified, and converted to a baseband signal. The transmitter converts a baseband digital signal to an analog signal, which is filtered and upconverted to an RF signal before being transmitted.

[0003] Non-linearity in the circuit blocks coupled to the output of the upconversion mixers, such as power amplifiers (PA) and driver amplifiers, often generate harmonics of the transmitted signal. Such harmonics, particularly the third and fifth harmonics, are undesired and should be kept below a certain threshold in order to meet the emission requirements. In the long term evolution (LTE) standard, such harmonics may couple to and desensitize an aggregated receiver associated with a different band when carrier aggregation is employed. Controlling the transmitter harmonics remains a challenge.

BRIEF SUMMARY

[0004] A communication device, in accordance with one embodiment of the present invention includes, in part, N upconverters, N amplifiers and at least one combiner. Each upconverter, made up of either M single balanced upconversion mixers or M/2 double-balanced upconversion mixers, receives M phases of a baseband signal to be transmitted. Each upconverter further receives a different one of N sets of phases of a local oscillator (LO) signal. Each of the N sets includes M different phases of the LO signal. Each amplifier is responsive to a different one of the upconverters to generate an amplified upconverted signal. The combiner combines the N amplified upconverted signals to generate an output signal. Undesired upconverted signal component at a frequency equal to a multiple of a sum of the LO signal frequency and the baseband signal frequency, or a multiple of a difference between the LO signal frequency and the baseband signal frequency is substantially suppressed from the output signal by selecting a gain of at least one of the amplifiers to be different from the gain of the remaining amplifiers. N and M are integers greater than 1.

[0005] In one embodiment, the communication device further includes, in part, a first filter receiving a baseband in-phase signal to generate a first set of filtered in-phase baseband signals to be transmitted, and a second filter receiving a baseband quadrature- phase signal to generate a second set of filtered quadrature -phase of the signals to be transmitted. In one embodiment, the baseband in-phase signal includes a first pair of complementary signals and the baseband quadrature-phase signal includes a second pair of complementary signals. In one embodiment N is 3 and M is 4.

[0006] In one embodiment, to eliminate a third harmonic, first and second amplifiers are selected to have an equal gain and a third amplifier is selected to have a gain larger than the gain of the first and second amplifiers. In one embodiment, the gain of the third

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amplifier is substantially 2& times the gain of the first and second amplifiers. In one embodiment, the gain of the third amplifier is substantially 2io times the gain of the first and second amplifiers.

[0007] In one embodiment, the four phases of the LO signal in a first set lead corresponding four phases of the LO signal in a second set by 45°. In one embodiment, the four phases of the LO signal in a third set lag corresponding four phases of the LO signal in the second set by 45°. In one embodiment, the four phases of the LO signal in the first are at 315, 135, 45, 225 degrees, the 4 phases of the LO signal in the second set are at 0, 180, 90, 270 degrees, and the 4 phases of the LO signal in the third set are at 45, 225, 135, 315 degrees.

[0008] A communication device, in accordance with another embodiment of the present invention includes, in part, N sets of upconverters and N sets of combiners. Each of the N set of upconverters includes Q upconverters. Each of the Q upconverters in each of the N sets receives M phases of a signal to be transmitted. Each of the Q upconverters in each of the N sets further receives one of Q*N sets of phases of a LO signal. Each of the Q*N sets includes M phases of the LO signal. In response, each of the Q upconverters generates an upconverted in-phase signal and an upconverted inverse signal. Each set of combiners is associated with a different one of the N sets of upconverters. A first combiner in each such set combines the N in-phase signals the first combiner receives from its associated upconverters. A second combiner in each set combines the N inverse signals the second combiner receives from its associated upconverters. Undesired upconverted signal component at a frequency equal to a multiple of a sum of the LO signal frequency and the baseband signal frequency, or a multiple of a difference between the LO signal frequency and the baseband signal frequency is substantially suppressed from the combined in-phase and inverse signals, Q, M and N are positive integers.

[0009] In one embodiment, the communication device further includes, in part, a first filter receiving a baseband in-phase signal to generate a first set of in-phase signals to be transmitted, and a second filter receiving a baseband quadrature-phase signal to generate a second set of filtered quadrature-phase of the signals to be transmitted. In one embodiment, the baseband in-phase signal includes a first pair of complementary signals and the baseband quadrature-phase signal includes a second pair of

complementary signals. In one embodiment, N and Q are equal to three. In one embodiment, NxQ sets of phases of the LO signal includes 5 distinct sets, and M is equal to 4.

[0010] In one embodiment, the communication device further includes, in part, N amplifiers each associated with a different one of the N sets of combiners. Each amplifier amplifies the upconverted signal and its inverse it receives from its associated set of combiners. In one embodiment, the gain of at least one of the amplifiers is

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substantially 26 times the gain of the remaining amplifiers. In one embodiment, the gain of at least one of the amplifiers is substantially 2io times the gain of the remaining amplifiers.

[0011] In one embodiment, the four phases of the LO signal in a first set lead corresponding four phases of the LO signal in a second set by 45°. In one embodiment, the four phases of the LO signal in a third set lag corresponding four phases of the LO signal in the second set by 45°. In one embodiment, the four phases of the LO signal in the first are at 315, 135, 45, 225 degrees, the 4 phases of the LO signal in the second set are at 0, 180, 90, 270 degrees, and the 4 phases of the LO signal in the third set are at 45, 225, 135, 315 degrees.

[0012] A method of communication, in accordance with one embodiment of the present invention includes, in part, applying M phases of a baseband signal to be transmitted to N upconverters, and applying a different one of N sets of phases of a LO signal to each of the N upconverters. Each of the N sets includes a different one of M phases of the LO signal. The method further includes, in part, applying an output signal of each of the N upconverters to a different one of N associated amplifiers to generate N amplified signals, selecting a gain of at least a first one of the N amplifiers to be different from a gain of a remaining one of the N amplifiers, and combining the N amplified signals to generate an output signal. N and M are integers greater than 1.

[0013] A method of communication, in accordance with another embodiment of the present invention includes, includes, in part, applying M phases of a baseband signal to be transmitted to N sets of upconverters, each set comprising Q upconverters. The M phases of the baseband signal are applied to each of the Q upconverters of each of the N sets. The method further includes, in part, applying to each of the Q upconverters of each of the N sets one of Q*N sets of phases of a LO signal. Each of the Q*N sets includes M phases of the LO signal. Each of the Q upconverters generates an upconverted signal and its inverse signal. The method further includes, in part, combining the N in-phase signals generated by the Q converters of each of the N sets thereby to generate N combined in-phase signals, and combining the N inverse signals generated by the Q converters of each of the N sets thereby to generate N combined inverse signals. Undesired upconverted signal component at a frequency equal to a multiple of a sum of the LO signal frequency and the baseband signal frequency, or a multiple of a difference between the LO signal frequency and the baseband signal frequency is substantially suppressed from the combined in-phase and inverse signals. Q, M and N are positive integers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Aspects of the disclosure are illustrated by way of example. In the accompanying figures, like reference numbers indicate similar elements, and: [0015] Figure 1 is a block diagram of a wireless communication device, in accordance with one embodiment of the present invention.

[0016] Figure 2 A is a block diagram of a number of components disposed in a transmit chain of a transmitter, in accordance with one exemplary embodiment of the present invention.

[0017] Figure 2B is a generalized block diagram of the transmit chain illustrated in Figure 2A, in accordance with one exemplary embodiment of the present invention.

[0018] Figure 3 A shows the phasors corresponding to a number of signals of Figure 2A at a fundamental frequency of (LO+BB) defined by the local oscillator frequency of LO and baseband frequency of BB), in accordance with one embodiment of the present invention.

[0019] Figure 3B shows the phasors corresponding to the signals of Figure 3 A at the third harmonic frequency of 3*(LO+BB), in accordance with one embodiment of the present invention.

[0020] Figure 3C shows the phasors corresponding to the signals of Figure 3 A at the fifth harmonic frequency of 5* (LO+BB), in accordance with one embodiment of the present invention.

[0021] Figure 4 A is a block diagram of a number of components disposed in the transmit chain of a transmitter, in accordance with one exemplary embodiment of the present invention.

[0022] Figure 4B is a generalized block diagram of the transmit chain illustrated in Figure 4A, in accordance with one exemplary embodiment of the present invention.

[0023] Figures 5A-5C show the phasors corresponding to a number of transmit signals of Figure 4A at a fundamental frequency of (LO+BB) defined by the local oscillator frequency of LO and baseband frequency of BB), in accordance with one embodiment of the present invention.

[0024] Figures 6A-6C show the phasors corresponding to the signals of Figures 5A- 5C at the third order spurious upconversion product frequency of (3*LO-BB), in accordance with one embodiment of the present invention. [0025] Figures 7A-7C show the phasors corresponding to the signals of Figures 5A- 5C at the fifth order spurious upconversion product frequency of (5*LO+BB), in accordance with one embodiment of the present invention.

[0026] Figure 8 is a flowchart for transmitting a signal, in accordance with one embodiment of the present invention.

[0027] Figure 9 is a flowchart for transmitting a signal, in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Several illustrative embodiments will now be described with respect to the accompanying drawings, which form a part hereof. While particular embodiments, in which one or more aspects of the disclosure may be implemented, are described below, other embodiments may be used and various modifications may be made without departing from the scope of the disclosure.

[0029] Figure 1 is a block diagram of a wireless communication device 50

(hereinafter alternatively referred to as device) used in a wireless communication system, in accordance with one embodiment of the present invention. Device 50 may be a cellular phone, a personal digital assistant (PDA), a modem, a handheld device, a laptop computer, and the like.

[0030] Device 50 may communicate with one or more base stations on the downlink (DL) and/or uplink (UL) at any given time. The downlink (or forward link) refers to the communication link from a base station to the device. The uplink (or reverse link) refers to the communication link from the device to the base station.

[0031] A wireless communication system may be a multiple-access system capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, spatial division multiple access (SDMA) systems, and the long term evolution (LTE) systems. [0032] Device 50 is shown as including, in part, frequency upconverter/modulator 10, digital to analog converter (DAC) 12, filter 14 and amplifier 16, which collectively form a transmission channel. Incoming digital signal 22 is first applied to DAC 12. The converted analog signal is filtered by filter 14, frequency upconverted with

upconverter/modulator 10 and its output further amplified by amplifier 16. The amplified signal generated by amplifier 16 may be optionally further amplified using a power amplifier 18 before being transmitted by antenna 20. In certain embodiments, the amplified signal at the output of each of the driver amplifier 16 and/or power amplifier 18 may also be filtered (not shown) before passing through other blocks.

[0033] Figure 2A is a block diagram of a number of components disposed in a transmit chain 24, in accordance with one exemplary embodiment of the present invention. Transmit chain 24 is shown as including, in part, filters 102, 104, quadrature upconverters 120, 122, 124, driver amplifiers 130, 132, 134, and combiners 140, 142. Transmit chain 24 is adapted to upconvert the frequency of the signals it receives and suppress spurious harmonics generated in driver amplifiers 130, 132, and 134, as described further below.

[0034] Filter 102 filters out undesired signals from the I-channel baseband signals I _bb and IBbb to generate filtered baseband signals Ibb_F and IBbb_F. Signals Ibb and IBbb are inverse (complement) of one another. Likewise, filter 104 filters out undesired signals from Q-channel baseband signals (¾ _b and QB _bb to generate filtered baseband signals Q _bb _F and QB _bb _F. The four filtered baseband signals ¾, _b _F, IB _bb _F, Q _bb _F and QB _bb _F that are 90° phase shifted with respect to one another are applied to each of the quadrature upconverters 120, 122, 124. As shown, quadrature upconverter 120 receives four phases 315, 135, 45, 225 of a local oscillator (not shown). Quadrature upconverter 122 receives four phases 0, 180, 90, 270 of the local oscillator. Quadrature upconverter 124 receives four phases 45, 225, 135, 315 of the local oscillator. Accordingly, the four phases of the LO signal received by quadrature upconverter 120 lead the corresponding phases of the LO signal received by quadrature upconverter 122 by 45°. Likewise, the four phases of the LO signal received by quadrature upconverter 124 lag the

corresponding phases of the LO signal received by quadrature upconverter 122 by 45°.

[0035] Quadrature upconverter 120 performs frequency upconversion to generate RF signals L, Qi; quadrature upconverter 122 performs frequency upconversion to generate RF signals I ₂ , Q ₂ ; and quadrature upconverter 124 performs frequency upconversion to generate RF signals I ₃ , (¾. Amplifier 130 amplifies signals I ₁ /Q ₁ to generate a pair of complementary signals A and AB; amplifier 132 amplifies signals I ₂ /Q ₂ to generate a pair of complementary signals B and BB; and amplifier 134 amplifies signals I3/Q3 to generate a pair of complementary signals C and CB.

[0036] Since the four phases of the local oscillator signal applied to quadrature upconverter 120 lead the corresponding phases of the local oscillator signal applied to quadrature upconverter 122 by 45°, signal Ii leads signal I ₂ by 45° and signal Qi leads signal Q ₂ by 45°. Therefore, signal A leads signal C by 45° and signal AB leads signal CB by 45°. Likewise, because the four phases of the local oscillator signal applied to quadrature upconverter 124 lag the corresponding phases of the local oscillator signal applied to quadrature upconverter 122 by 45°, signal B lags signal C by 45° and signal BB lags signal CB by 45°.

[0037] Figure 2B is a generalized block diagram of the transmit chain illustrated in Figure 2A, in accordance with one exemplary embodiment of the present invention. As illustrated, in general, the transmit chain 26 may include M filters 202 each receiving one of the M input signals and output one of the output signals outi through out _M . Each output signal (e.g., outi) may include a signal and its inverse. The output signals may enter the generalized upconverters 222 ₁ through 222N. Each of the generalized upconverters 222 may include M/2 double balanced mixers. Output of the N

upconverters 222 may be amplified with N amplifiers 224 ₁ through 224N. The amplified signals may then be combined with the generalized combiner 226 to generate output 228.

[0038] Figure 3A shows three phasors corresponding to signals A, B and C having a fundamental frequency defined by the local oscillator (LO) frequency of LO and baseband frequency of BB, namely LO+BB. As seen in Figure 3 A, at this fundamental frequency, signal A leads signal C by 45° and signal B lags signal C by 45°. Figures 3B and 3C show the same three phasors respectively at the third harmonic frequency of 3*(LO+BB), and fifth harmonic frequency of 5*(LO+BB). For the third harmonic, the difference between phases of signals C and A, or C and B is 3*45°=135°. For the fifth harmonic, the difference between phases of signals C and A, or C and B is 5*45°=225°. [0039] Referring to Figure 3A, it is seen that the three phasors corresponding to signals A, B, and C at the fundamental and desired frequency of LO+BB reinforce one another. Therefore, the output signal Outp of combiner 140, which is generated by combining/adding signals A, B , C, is enhanced at the fundamental frequency.

[0040] Referring to Figure 3B, it is seen that in order to substantially suppress the third harmonic, the sum of the projections (magnitudes) of phasors A and B along the x- axis has to be equal to the magnitude of phasor C along the same axis. Assuming phasors A and B have a length of 1 , because the angle between phasors C and A as well as the angle between phasors C and B is 135°, the x-component of each of phasors A and B has a length (value) of — . Therefore, the sum of the x-components of signals A and B at the third harmonic frequency is equal to V2. Consequently, to substantially eliminate the third harmonic, phasor C is selected to have a length that is V2 times the lengths of phasors A and B. This causes the three phasors to cancel each other along both the x and y axes. In order for phasor C to have a length (size) that is V2 times the

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length of phasors A and B, amplifier 132 is selected to have a gain that is 2& times the gains of amplifiers 130, 134. Consequently, if amplifiers 130, 134 have a gain of G,

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amplifier 132 has a gain of 2e*G.

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[0041] When amplifier 132 is selected to have a gain of 2e*G, the third harmonic of signals I ₂ and Q ₂ is amplified by a factor of (2<5 ) ³ — which is equal to V2. In other words, because amplifiers 130, 134 have a gain of G, whereas amplifier 132 has a gain

1

of (2e ), the third harmonic of signal C has a magnitude that is greater than that of signals A and B by a factor of (2& ) ³ which is equal to V2. Likewise, the third harmonic of signal CB has a magnitude that is larger than that of signals AB and BB by a factor of V2. Accordingly, as described above, output signal Outp that is generated by

combining/adding signals A, B, C, has a substantially reduced component at the third harmonic frequency of 3* (LO+BB). Likewise, output signal Outn that is generated by combining/adding signals AB, BB, CB, has a substantially reduced component at the third harmonic frequency of 3* (LO+BB).

[0042] Referring to Figure 3 C, it is seen that the y-components of signals A and B cancel one another. Therefore, in order to substantially suppress the fifth harmonic, the sum of the x-components of phasors A and B has to be equal to the x-component of phasor C. Assuming phasors A and B have a length of 1, because the angle between phasors C and A as well as the angle between phasors C and B is 225°, the magnitude of each of phasors A and B along the x-axis is— . Consequently, to substantially eliminate the fifth harmonic, phasor C is selected to have a length that is V2 times the length of phasors A and B. This causes the three phasors to cancel each other along both the x and y axes. For phasor C to have a length that is V2 times the length of phasors A and B, amplifier 132 is selected to have a gain that is 2io times the gains of amplifiers 130, 134. Consequently, if amplifiers 130, 134 have a gain of G, amplifier 132 has a gain of

2^*G.

[0043] When amplifier 132 is selected to have a gain of 2io*G, the fifth harmonic of

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signals I ₂ and Q ₂ is amplified by a factor of (2 o ) ⁵ — which is equal to V2. In other words, because amplifiers 130, 134 have a gain of G, whereas amplifier 132 has a gain of (210 ), the fifth harmonic of signal C has a magnitude that is larger than that of

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signals A and B by a factor of (2 o ) ⁵ which is equal to V2. Likewise, the fifth harmonic of signal CB has a magnitude that is larger than that of signals AB and BB by a factor of V2. Accordingly, output signal Outp that is generated by combining/adding signals A, B, C (using combiner 140) has a substantially reduced component at the fifth harmonic frequency of 5*(LO+BB). Likewise, output signal Outn that is generated by

combining/adding signals AB, BB, CB (using combiner 142) has a substantially reduced component at the fifth harmonic frequency of 5*(LO+BB). Consequently, in accordance with the present invention, by adjusting the gain of amplifier 132 relative to the gains of amplifiers 130 and 134, the undesired harmonics caused by non-linearity of the amplifiers is substantially suppressed.

[0044] In one embodiment, each of the frequency upconverters 120, 122, 124 may be a composite harmonic-rejective frequency upconverter that, in turn, includes a multitude of upconverters. Figure 4A is a block diagram of another exemplary embodiment of a frequency upconverter. Transmit chain 24 of Figure 4A is shown as including, in part, filters 102, 104, quadrature upconverters 120i, 120 ₂ , 120 ₃ collectively forming upconverter 120, quadrature upconverters 122 _ls 122 ₂ , 122 ₃ collectively forming upconverter 122, quadrature upconverters 124 _ls 124 ₂ , 124 ₃ collectively forming upconverter 124, driver amplifiers 130, 132, 134, and combiners 202, 204, 206, 208, 210, 212, 140, 142.

[0045] Transmit chain 24 of Figure 4A is adapted to upconvert the frequency of the signals it receives and suppress the third harmonic frequency of 3*(LO+BB) or fifth harmonic frequency of 5*(LO+BB), as described above in reference to Figures 2 and 3A-3C. Transmit chain 24 of Figure 4 A is further adapted to suppress the third order spurious mixing product of 3*LO-BB caused by the upconverters, the fifth order spurious mixing product of 5*LO+BB caused by the upconverters, as well as the undesired counter-IM3 product of LO-3*BB caused by the driver amplifiers. While the embodiment of Figure 4A is described with reference to a frequency upconversion circuit having 3 sets of upconverters 120, 122, 124 each set having 3 upconverters (for a total of 9 upconverters), it is understood that other embodiments may have N sets of upconverters with each set including Q upconverters, where N and Q are positive integers. Furthermore, while the frequency upconversion circuit of Figure 4A is shown as receiving 9 sets of phases of the LO signal with each set including 4 different phases of the LO signal, it is understood that other embodiments may receive N ^X Q sets of phases of a LO signal with each set including M different phases of the LO signal, where N, Q and M are positive integers. For certain embodiments, some of the N ^X Q sets of phases of the LO signal may be distinct and some of the sets may be similar to one another. For example, if N=3 and Q=3, out of 9 sets of phases of the LO signal, 5 sets may be distinct and 4 sets may be duplicate of the other sets.

[0046] Filter 102 filters out undesired signals from the I-channel baseband signals Ibb and IBbb to generate filtered baseband signals Ibb_F and IB _b b_F. Signals Ι¾ and IB _b b are inverse of one another. Likewise, filter 104 filters out undesired signals from Q-channel baseband signals Qbb and QBbb to generate filtered baseband signals Qbb_F and QBbb_F. The four filtered baseband signals Ibb_F, IBbb_F, Qbb_F and QBbb_F that are 90° phase shifted with respect to one another are applied to each of the quadrature upconverters 120i, 120 ₂ , 120 ₃ , 122i, 122 ₂ , 122 ₃ , 124 _h 124 ₂ , 124 ₃ .

[0047] As shown, upconverter 120i receives four phases 270, 90, 0, 180 of the local oscillator; upconverter 120 ₂ receives four phases 315, 135, 45, 225 of the local oscillator; upconverter 120 ₃ receives four phases 0, 180, 90, 270, of the local oscillator; upconverter 122 ₁ receives four phases 315, 135, 45, 225 of the local oscillator;

upconverter 122 ₂ receives four phases 0, 180, 90, 270 of the local oscillator;

upconverter 122 ₃ receives four phases 45, 225, 135, 315 of the local oscillator;

upconverter 124 ₁ receives four phases 0, 180, 90, 270 of the local oscillator;

upconverter 124 ₂ receives four phases 45, 225, 135, 315 of the local oscillator; and upconverter 124 ₃ receives four phases 90, 270, 180, 0 of the local oscillator (LO).

[0048] Accordingly, the four phases of the LO signal received by upconverter 120i lead the corresponding phases of the LO signal received by upconverter 120 ₂ by 45°, and the four phases of the LO signal received by upconverter 120 ₃ lag the corresponding phases of the LO signal received by quadrature upconverter 120 ₂ by 45°. Similarly, the four phases of the LO signal received by upconverter 122 ₁ lead the corresponding phases of the LO signal received by upconverter 122 ₂ by 45°, and the four phases of the LO signal received by upconverter 122 ₃ lag the corresponding phases of the LO signal received by quadrature upconverter 122 ₂ by 45°. Likewise, the four phases of the LO signal received by upconverter 124 ₁ lead the corresponding phases of the LO signal received by upconverter 124 ₂ by 45°, and the four phases of the LO signal received by upconverter 124 ₃ lag the corresponding phases of the LO signal received by quadrature upconverter 124 ₂ by 45°.

[0049] Furthermore, the four phases of the LO signal received by upconverter 120; lead the corresponding phases of the LO signal received by quadrature upconverter 122; by 45°, where i is an integer varying from 1 to 3 in this exemplary embodiment. For example, the four phases 315, 135, 45, 225 of the LO signal received by upconverter 120 ₂ lead the corresponding four phases 0, 180, 90, 270 of the LO signal received by quadrature upconverter 122 ₂ by 45°. Likewise, the four phases of the LO signal received by upconverter 124; lag the corresponding phases of the LO signal received by quadrature upconverter 122; by 45°. For example, the four phases 45, 225, 135, 315 of the LO signal received by upconverter 124 ₂ lag the corresponding phases 0, 180, 90, 270 of the LO signal received by quadrature upconverter 122 ₂ by 45°.

[0050] Upconverter 120i performs frequency upconversion to generate upconverted in-phase and inverse RF signals Gi, G ₂ ; upconverter 120 ₂ performs frequency upconversion to generate upconverted in-phase and inverse RF signals Hi, H ₂ ;

upconverter 120 ₃ performs frequency upconversion to generate upconverted in-phase and its inverse RF signals L, I _2; upconverter 122 ₁ performs frequency upconversion to generate upconverted in-phase and inverse RF signals D _ls D ₂ ; upconverter 122 ₂ performs frequency upconversion to generate upconverted in-phase and inverse RF signals E _ls E ₂ ; upconverter 122 ₃ performs frequency upconversion to generate upconverted in-phase and inverse RF signals F _ls F ₂ ; upconverter 124 ₁ performs frequency upconversion to generate upconverted in-phase and inverse RF signals Ji, J ₂ ; upconverter 124 ₂ performs frequency upconversion to generate upconverted in-phase and inverse RF signals K _ls K ₂ ; and upconverter 124 ₃ performs frequency upconversion to generate upconverted in-phase and inverse RF signals L _ls L ₂ .

[0051] Combiner 202 is adapted to add/combine signals Gi, Hi, Ii to generate signal M; combiner 204 is adapted to add/combine signals G ₂ , H ₂ , h to generate signal N; combiner 206 is adapted to add/combine signals D _ls E _ls Fi to generate signal O;

combiner 208 is adapted to add/combine signals D ₂ , E ₂ , F ₂ to generate signal p;

combiner 210 is adapted to add/combine signals Ji, K _ls Li to generate signal S; and combiner 212 is adapted to add/combine signals J ₂ , K ₂ , L ₂ to generate signal T.

Amplifier 130 amplifies signals M and N to generate a pair of complementary signals A and AB; amplifier 132 amplifies signals O and P to generate a pair of complementary signals B and BB; and amplifier 134 amplifies signals S and T to generate a pair of complementary signals C and CB.

[0052] Since the four phases of the local oscillator signal applied to quadrature upconverter 120i lead the corresponding phases of the local oscillator signal applied to quadrature upconverter 120 ₂ by 45°, signals Gi and G ₂ respectively lead signals Hi and H ₂ by 45°. Likewise, because the four phases of the local oscillator signal applied to quadrature upconverter 120 ₃ lag the corresponding phases of the local oscillator signal applied to quadrature upconverter 120 ₂ by 45°, signals Ii and I ₂ respectively lag signals Hi and H ₂ by 45°. For the same reason, signals Di and D ₂ respectively lead signals Ei and E ₂ by 45°, and signals Fi and F ₂ respectively lag signals Ei and E ₂ by 45°. Likewise, signals Ji and J ₂ respectively lead signals Ki and K ₂ by 45°, and signals Li and L ₂ respectively lag signals Ki and K ₂ by 45°.

[0053] Figure 4B is a generalized block diagram of the transmit chain illustrated in Figure 4A, in accordance with one exemplary embodiment of the present invention. As illustrated, in general, the transmit chain 28 may include M filters 202 each receiving one of the M input signals and output one of the output signals outi through out _M . Each output signal (e.g., outi) may include a signal and its inverse. The output signals may enter each of the N sets of the generalized upconverters (e.g., 440i through 440Q). Each of the generalized upconverters 440 may include M/2 double balanced mixers or M single balanced mixers. Output of the Q upconverters 440 may be combined with combiner 450 before being amplified with amplifier 2241. Outputs of the N amplifiers 2241 through 224 _N may then be combined with the generalized combiner 226 to generate output 228.

[0054] Figure 5 A shows three phasors associated with signals I _ls Gi and Hi having a fundamental frequency defined by the local oscillator (LO) frequency of LO and baseband frequency of BB, namely LO+BB. As seen in Figure 5 A, at this fundamental frequency, signal Gi leads signal Hi by 45° and signal Ii lags signal Hi by 45°. Figure 5B shows three phasors associated with signals E _ls Fi and Di having a fundamental frequency of LO+BB. As seen in Figure 5B, at this fundamental frequency, signal Di leads signal Ei by 45° and signal Fi lags signal Ei by 45°. Figure 5C shows three phasors associated with signals Ji, Ki and Li having a fundamental frequency of LO+BB. As seen in Figure 5C, at this fundamental frequency, signal Ji leads signal Ki by 45° and signal Li lags signal Ki by 45°.

[0055] Figure 6A shows the three phasors associated with signals Gi, Hi, L at the spurious upconversion mixing product frequency of (3*LO-BB). The value (amplitude) of signal Hi is selected to be V2 times greater than the value of each of signals Gi and L. Thus, the y-component of signal Hi cancels signal G _ls and the x-component of signal Hi cancels signal L. Figure 6B shows the three phasors associated with signals D _ls Ei, Fi at the spurious upconversion mixing product frequency of (3*LO-BB). The value of signal Ei is selected to be V2 times greater than the value of each of signals Di and Fi. Thus, the y-components of signals Di and Fi cancel each other. Furthermore, the sum of the x- components of signals Di and Fi cancel signal Ei. Figure 7C shows the three phasors associated with signals Ji, KI, Li at the spurious upconversion mixing product frequency of (3*LO-BB). The value of signal Ki is selected to be V2 times greater than the value of each of signals Li and Ji. Thus, the x-component of signal Ki cancels signal Ji, and the y-component of signals Ki cancels signal Li. Accordingly, the spurious upconversion mixing product at frequency (3*LO-BB) is substantially reduced at (i) the outputs M and N of combiners 202, 204, (ii) the outputs O and P of combiners 206, 208; and (iii) the outputs S, T of combiners 201 , 212. In other words, in accordance with one aspect of the present invention, the spurious upconversion mixing products at frequency (3*LO-BB) is canceled or substantially reduced at the outputs of combiners, i.e., at the inputs of amplifiers 130, 132, 134.

[0056] Figure 7A shows the three phasors associated with signals G _{l s} Ii at the spurious upconversion product frequency of (5*LO+BB). The value of signal Hi is selected to be V2 times greater than the value of each of signals Gi and Hi. Thus, the y- component of signal Hi cancels signal Gi, and the x-component of signal Hi cancels signal 1 _\ . Figure 7B shows the three phasors associated with signals D _{l s} Ei, Fi at the spurious upconversion product frequency of (5*LO+BB). The value of signal Ei is selected to be V2 times greater than the value of each of signals Di and Fi. Thus, the y- components of signals Di and Fi cancel each other. Furthermore, the sum of the x- components of signals Di and Fi cancel signal Ei.

[0057] Figure 7C shows the three phasors associated with signals Ji, Kl , Li at the spurious upconversion product frequency of (5*LO+BB). The value of signal Ki is selected to be 2 times greater than the value of each of signals Li and Ji. Thus, the x- component of signal Ki cancels signal Ji, and the y-component of signals Ki cancels signal Li. Accordingly, the spurious upconversion products at frequency (5*LO+BB) is substantially canceled at (i) the outputs M and N of combiners 202, 204, (ii) the outputs O and P of combiners 206, 208; and (iii) the outputs S, T of combiners 201 , 212. In other words, in accordance with one aspect of the present invention, the spurious upconversion product at frequency (5*LO+BB) is canceled or substantially reduced at the outputs of combiners, i.e., at the inputs of the amplifiers.

[0058] It should be noted that the proposed method also rejects undesired components at frequency LO-3BB. The undesired components at frequency LO-3BB are generated because of the presence of third order nonlinearity in amplifiers 130,132, 134 as a result of intermodulation of input signals with spectral components at LO+BB and 3*LO-BB. The embodiment as illustrated in Figure 4A, rejects 3*LO-BB components by design at the combiner outputs 202, 204, 206, 208, 210 and 212. As a result of this rejection of the 3*LO-BB component, no substantial LO-3*BB product can be generated at the outputs of amplifiers 130, 132, 134. [0059] Figure 8 is a flowchart 200 for a communication method, in accordance with one embodiment of the present invention. To perform the communication, M phases of a signal to be transmitted are applied 202 to N upconverters. One of N sets of phases of a LO signal are also applied 204 to each of the N upconverters. Each of the N sets of phases includes a different one of M phases of the LO signal. The output of each upconverter is applied 206 to an associated amplifier to generate N amplified signals. The gain of at least one of the amplifiers is set 208 to a value that is different from the gain of the remaining amplifiers. The amplified signals are combined 216 to generate an output signal that has a substantially reduced harmonics of the upconverted signal to be transmitted.

[0060] Figure 9 is a flowchart 200 for a communication method, in accordance with one embodiment of the present invention. To perform the communication, M phases of a signal to be transmitted are applied 304 to N sets of upconverters. Each of the N sets includes Q upconverters. As illustrated, the M phases of the signal are applied to each of the Q upconverters of each of the N sets. One of NxQ sets of phases of a local oscillator signal are also applied 306 to each of the N ^X Q upconverters. Each of the N ^X Q sets includes M phases of the LO signal. Each of the Q upconverters generates an upconverted in-phase signal and an upconverted inverse signal in response. Thereafter, the Q in-phase signals generated by the Q upconverters of each of the N sets are combined 308 to generate N combined in-phase signals. The Q inverse signals generated by the Q upconverters of each of the N sets are also combined 310 to generate N combined inverse signals.

[0061] The above embodiments of the present invention are illustrative and not limitative. The embodiments of the present invention are not limited by the number of upconverters, the number of sets of LO phases, or the number of LO phases in each such set. Nor are the embodiments of the present invention limited by any particular phases of the local oscillator used in each set. Other additions, subtractions or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.